Moral duties are often described in terms of rigid requirements to perform, or refrain from performing, actions of certain specific types. In various theological traditions this point is often expressed in terms of the demands God places upon His creatures. However, there are several important ways, as Kant, Mill, and others have noted, in which the fulfillment of duty admits of options. In this paper an effort is made to offer a precise characterization of these ways. On this basis it is concluded that many duties are not of the form in which duties are commonly characterized